Include ERT_SIMULATION_MODE in metadata

[mferrera]

Currently we only store the experiment uuid in the metadata.

fmu-dataio/src/fmu/dataio/_model/fields.py

Lines 214 to 219 in 8d293da

	class Ert(BaseModel):
	"""The ``fmu.ert`` block contains information about the current ert run."""
	experiment: Optional[Experiment] = Field(default=None)
	"""Reference to the ert experiment.
	See :class:`Experiment`."""

ert exposes _ERT_SIMULATION_MODE and we know it

fmu-dataio/src/fmu/dataio/providers/_fmu.py

Lines 76 to 79 in 8d293da

	class FmuEnv(Enum):
	EXPERIMENT_ID = auto()
	ENSEMBLE_ID = auto()
	SIMULATION_MODE = auto()

but as of now do nothing with it. Storing this will enable some extra contextual inference, i.e. adds a bit to #299

It's not clear if this should be in case metadata, object metadata, or both. Or what might go wrong if these don't align given the different forms of rerunning a realization.